Some service-oriented architecture (SOA) designs impose high concurrency/low latency requirements on primary data store for read and write operations. Read-intensive activity can be scaled by offloading queries from the primary (source-of-truth) data store to a secondary (caching) store. Write=intensive activity, on the other hand, must always modify the primary/source-of-truth. Accordingly, the primary data store must be sharded to meet write scale requirements. This patent proposal describes a pattern for implementing a horizontally scalable sharded primary data store. The pattern provides immediate consistency guarantees to the primary and secondary data stores, as well as an additional “external global index”. The external global index enforces uniqueness constraints within a sharded domain and enables applications to use a business defined key(s) to navigate to the correct shard within a primary's data domain.